1. Field of the Invention
The present invention relates to a disk having a recordable and reproducible area and an area in which fixed information dedicated to reproduction is recorded, and a disk recording apparatus which performs recording onto the disk.
2. Description of the Related Art
In recent years, due to the ability to hold a large capacity of data, an optical disk capable of recording information has been becoming important for accumulating audio data, video data, and various information equipment data. Under this circumstance, there is a demand for a larger capacity of an optical disk. In order to meet this demand, the density of recorded information on an optical disk needs to be increased. The information density on an optical disk is determined by a pitch of an information track and an information density in a track direction (i.e., linear density of information). Thus, in order to improve the information density on an optical disk, it is required to narrow a track pitch and increase a linear density.
An optical disk can be used for various purposes. For example, in the case of using an optical disk as a medium for supplying software such as an operating system and a basic dictionary or software for games, if a read-only optical disk is produced in such a manner that data is recorded in the form of concave or convex pits, optical disks can be replicated in large quantity at low cost.
On the other hand, there is a demand that a user can append or write desired data to read-only data recorded by a software supplier in accordance therewith. Thus, in order to meet this demand, it is required that one optical disk has an area in which read-only data is recorded and a recordable and reproducible area.
In the case of providing the above-mentioned two areas in one optical disk for recording/reproduction, read-only data is previously recorded on concave grooves and convex tracks before shipping, and this recorded area may be used only for reproducing data. In this case, read-only data is required to be recorded onto each disk, which is a time-consuming task and increases cost.
In order to solve this problem, an optical disk has been proposed, in which required data is recorded in an area of the optical disk in the form of concave or convex pits, and the remaining area is made recordable (e.g., Japanese Laid-open Publication No. 63-20769). In this case, it is not required to record required data on each disk, which allows mass-production of optical disks by, for example, injection, resulting in a decrease in cost.
The most popular disk as a ROM disk is a CD or is DVD-ROM disk. In these disks, in order to achieve a large capacity, concave or convex pits are continuously recorded at a constant linear speed for tracing tracks. Needless to say, data is also required to be reproduced by rotating a disk at a constant linear speed.
In the case of constructing a disk having a ROM portion and a RAM portion, a format of the ROM portion should be made identical with that of a CD or a DVD-ROM disk for the following reason: when a disk having a ROM portion and a RAM portion is mistakenly inserted into a drive device which only reads data from a CD or a DVD-ROM disk, if the format of the ROM portion is identical with that of a CD or a DVD-ROM, the drive device can recognize the mistakenly inserted disk.
Now, a method for reproducing data from a CD or a DVD-ROM disk by a drive device will be described.
As for reproduction of the above-mentioned disk, a pick-up head is moved to an area called a lead-in, and information called control data required for reproducing the disk is read. The procedure to the time when information starts being read is as follows.
First, a disk surface is focused by controlling the position of a lens of the pick-up head. Secondly, tracking is performed so that pit strings are continuously read by controlling a traverse mechanism and the lens. Thirdly, a particular period (e.g., the longest interval) of a reproduction signal input to a reproduction circuit is detected, and a rotation speed of a motor is controlled. Fourthly, when rotation variations are stopped, and a signal becomes able to be reproduced at a constant linear speed, a clock synchronized with the reproduction signal is generated, and data is read on the basis of the clock.
However, in the disk having a RAM portion and a ROM portion in which concave or convex pits are continuously recorded at a constant linear speed as described above, a number of operations are required to be performed successively during boot-up of the disk before data is read. Thus, such a disk has a disadvantage of a long boot-up time.
Furthermore, the ROM portion is recorded by a short wavelength cutting machine, so that the linear density can be made higher, compared with that of the RAM portion.
In contrast, the RAM portion has an area in which data is recorded and an area in which data is not recorded, and a sector ID is composed of pre-pits generally called a header. In the header, in addition to address information, a VFO signal for assisting an operation of a PLL (phase-locked loop) circuit, an address mark which is a synchronization signal of address information, etc. are placed, whereby the redundancy of the RAM portion is higher than that of the ROM portion.
However, in a conventional optical disk such as a CD or a DVD-ROM disk, the number of sectors included in one track of the ROM portion is equal to that included in one track of the RAM portion. In this case, the sector format of the ROM portion is identical with that of the RAM portion with high redundancy, so that the recording density of the ROM portion cannot be made high.
Furthermore, in a conventional optical disk, the number of sectors included in one track is equal from an inner track to an outer track in the RAM portion, so that the recording density is lower in the outer track than in the inner track, and the recording density cannot be made high.